Data from: Studies in Lichens and Lichenicolous Fungi – no. 18: resolution of three names introduced by Degelius and Magnusson based on material from the Great Smoky Mountains

Arthonia biseptata is shown to be a species of Mycoporum, likely narrowly endemic to high elevations of the southern Appalachian Mountains and the new combination M. biseptatum is proposed. Lecidea degelii is shown to apply to the sorediate morphotype of Porpidia albocaerulescens. The results of molecular phylogenetic analyses of nrITS and mtSSU sequence data of sorediate and esorediate populations of P. albocaerulescens are presented. These analyses recovered the sorediate and esorediate morophotypes together in a single clade as strongly-supported monophyletic entities. As a result the new combination Porpidia degelii is proposed, the species illustrated, and the North American distribution of P. degelii with respect to P. albocaerulescens is discussed. These data strongly refute the notion that "species pairs" do not exist in Porpidia. Lecidea subtilis is placed in synonymy with Pyrrhospora varians.